Add e2e tests for role promotion management

What does this MR do and why?

This implements #462689

Here we're adding e2e tests that covers the main user flows for non-billable promotion management

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

N/A

How to set up and validate locally

To run the e2e test locally:

1. For more details check out the readme file
2. cd gitlab-development-kit/gitlab/qa
3. bundle install
   • You might need to comment this line in the Gemlock file to avoid errors
4. QA_GITLAB_URL="<your-gdk-url>" bundle exec rspec qa/specs/features/ee/browser_ui/11_fulfillment/utilization/member_management_spec.rb
   • You might need to remove the only: { pipeline: %i[staging staging-canary] } to run the tests locally
   • You might also need to give your gdk a fresh start every now and then: gdk stop && gdk kill && gdk start